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Low-Resolution Spectroscopy of Gamma-Ray Burst Optical Afterglows: Biases in the Swift Sample

Low-Resolution Spectroscopy of Gamma-Ray Burst Optical Afterglows: Biases in the Swift Sample

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Low-Resolution Spectroscopy of Gamma-Ray Burst Optical Afterglows: Biases in the Swift Sample

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  1. Low-Resolution Spectroscopy of Gamma-Ray Burst Optical Afterglows: Biases in the Swift Sample (ApJ Supplement, 2009, 185, 526-573) PalliJakobsson Centre for Astrophysics & Cosmology University of Iceland

  2. Low-Resolution Spectroscopy of Gamma-Ray Burst Optical Afterglows: Biases in the Swift Sample (ApJ Supplement, 2009, 185, 526-573) PalliJakobsson Centre for Astrophysics & Cosmology University of Iceland

  3. The dark burst diagram (βOX) Jakobsson et al. (2004)

  4. Definition of βOX Optical X-ray Sari et al. (1998)

  5. Definition of βOX 2.0 < p < 2.5 Optical X-ray Sari et al. (1998)

  6. The dark burst diagram (βOX) Swift Identification of Dark Gamma-Ray Bursts: Jakobsson et al. (2004)

  7. The dark burst diagram (βOX)

  8. The sample 1. A Swift-detected GRB with t90 > 2 s. 2. XRT afterglow position distributed within 12 hours. 3. Small foreground Galactic extinction: AV < 0.5 mag. 4. Favorable declination: -70° < δ < 70°. 5. Sun-to-field distance larger than 55°. March 2005 – September 2008: 146 GRBs 75% have an optical/NIR afterglow

  9. The 3 sub-samples 1. GRBs with redshifts measured from OA spectroscopy. 72 • GRBs with detected optical/NIR afterglow, but no • afterglow-based redshift. 35 3. GRBs with no detection of the OA. 39

  10. The dark burst diagram (βOX) [z from OA] 14% [OA but no z] 38% [no OA] >39% 080913 (z = 6.7) 050904 (z = 6.3)

  11. XRT excess absorption distribution KS test probability (1 and 2): 2 x 10-3 KS test probability (1 and 3): 7 x 10-7

  12. βOX vs. X-ray excess absorption dark bursts

  13. Redshift distribution: 146 GRBs Grupe et al. (2007) < 18% @ z > 7 <z> = 2.2

  14. Cumulative redshift distribution